System and Method for Decreasing an Initial Buffering Period of an Adaptive Streaming System

ABSTRACT

System and methods for selecting one of the alternative streams of encoded media from a group of alternative streams of encoded media for use during start-up of playback of the encoded media in accordance with embodiments of this invention are disclosed. The systems and methods begin by determining an estimated stability period for a current bandwidth of a communicative connection between the playback device and a remote system providing the alternative streams of encoded. A test process is then performed on the streams of encoded media to select one of streams of encoded media that provides portions of said encoded media such that an underflow condition does not occur during the estimated stability period. The streaming of encoded media is then commenced by requesting the portions of encoded media be transmitted from the remote server using the selected stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. patent applicationSer. No. 15/937,715, filed Mar. 27, 2018, entitled “System and Methodfor Decreasing an Initial Buffering Period of an Adaptive StreamingSystem” to Shivadas et al. and will issue as U.S. Pat. No. 10,979,782,which is a continuation of U.S. patent application Ser. No. 13/631,017,filed Sep. 28, 2012, entitled “System and Method for Decreasing anInitial Buffering Period of an Adaptive Streaming System” to Shivadas etal. and issued as U.S. Pat. No. 9,936,267, which claims priority to U.S.Provisional Patent Application No. 61/696,095, filed Aug. 31, 2012,titled “System and Method for Decreasing an Initial Buffering Period ofan Adaptive Streaming System”, the disclosures of which are incorporatedherein by reference.

FIELD OF THE INVENTION

This invention generally relates to start-up of playback of an encodedmedia in an adaptive streaming system. More particularly, this inventionrelates to systems and methods that can reduce the amount of encodedmedia buffered by a playback device prior to starting playback of themedia.

BACKGROUND OF THE INVENTION

The term streaming media describes the playback of media on a playbackdevice, where the media is stored on a server and continuously sent tothe playback device over a network during playback. For purposes of thisdiscussion, media and/or encoded media is defined as data of a work thatincludes video, audio, pictures, or another type of presentation thatmay be displayed, played or in some other way presented by a playbackdevice. Typically, the playback device stores a sufficient quantity ofmedia in a buffer at any given time during playback to preventdisruption of playback due to the playback device completing playback ofall the buffered media prior to receipt of the next portion of media.Adaptive bit rate streaming or adaptive streaming involves detecting thepresent streaming conditions (e.g. the user's network bandwidth and CPUcapacity) in real time and adjusting the quality of the streamed mediaaccordingly. Typically, the source media is encoded at multiple bitrates and the playback device or client switches between streaming thedifferent encodings depending on available resources.

Adaptive streaming solutions typically utilize either Hypertext TransferProtocol (HTTP), published by the Internet Engineering Task Force andthe World Wide Web Consortium as RFC 2616, or Real Time StreamingProtocol (RTSP), published by the Internet Engineering Task Force as RFC2326, to stream media between a server and a playback device. HTTP is astateless protocol that enables a playback device to request a byterange within a file. HTTP is described as stateless, because the serveris not required to record information concerning the state of theplayback device requesting information or the byte ranges requested bythe playback device in order to respond to requests received from theplayback device. RTSP is a network control protocol used to controlstreaming media servers. Playback devices issue control commands, suchas “play” and “pause”, to the server streaming the media to control theplayback of media files. When RTSP is utilized, the media server recordsthe state of each client device and determines the media to stream basedupon the instructions received from the client devices and the client'sstate.

In adaptive streaming systems, the source media is typically stored on amedia server as a top level index file pointing to a number of alternatestreams that contain the actual video and audio data. Each stream istypically stored in one or more container files. Different adaptivestreaming solutions typically utilize different index and mediacontainers. The Synchronized Multimedia Integration Language (SMIL)developed by the World Wide Web Consortium is utilized to create indexesin several adaptive streaming solutions including IIS Smooth Streamingdeveloped by Microsoft Corporation of Redmond, Washington, and FlashDynamic Streaming developed by Adobe Systems Incorporated of San Jose,Calif. HTTP Adaptive Bitrate Streaming developed by Apple ComputerIncorporated of Cupertino, Calif. implements index files using anextended M3U playlist file (.M3U8), which is a text file containing alist of URIs that typically identify a media container file. The mostcommonly used media container formats are the MP4 container formatspecified in MPEG-4 Part 14 (i.e. ISO/IEC 14496-14) and the MPEGtransport stream (TS) container specified in MPEG-2 Part 1 (i.e. ISO/IECStandard 13818-1). The MP4 container format is utilized in IIS SmoothStreaming and Flash Dynamic Streaming. The TS container is used in HTTPAdaptive Bitrate Streaming.

When a playback device commences adaptive bitrate streaming, theplayback device typically starts by requesting portions of media fromthe lowest bitrate streams (where alternative streams are available). Asthe playback device downloads the requested media, the playback devicecan measure the available bandwidth. In the event that there isadditional bandwidth available, the playback device can switch to higherbitrate streams.

To start playback of the encoded media, the playback device oftenattempts to buffer an adequate amount of the requested encoded media bereceived and stored to provide a minimum amount of playback time priorto commencing the playback. Buffering encoded media can assure thatthere are no underflow conditions during playback. An underflowcondition is when the playback device does not have the next portion ofencoded media needed to continue the playback. However, the acquisitionof an adequate amount of encoded media usually causes a delay in thestart of playback of the encoded media by the device. This is typicallynot a problem when the playback is only periodically started and/orre-started.

However, recently devices such as tablets and other mobile playbackdevices have made it easier for users to search the encoded media andre-start the playback at various points in the playback. As such, theconventional start-up requiring an adequate amount of encoded media maycause unsatisfactory pauses or delays in presentation of the playback.As such, those skilled in the art are constantly striving to provide aplayback start-up that requires less of the encoded media prior tocommencement of the playback to minimize the time needed for a startand/or re-start of the playback.

SUMMARY OF THE INVENTION

Systems and methods for decreasing an initial buffering period in anadaptive bitrate system in accordance with embodiments of this inventionare disclosed. In accordance with some embodiments, a playback deviceselects one of set of alternative streams for start-up of playback ofencoded media from a playback position within the encoded media in thefollowing manner. The playback device begins by determining an estimatedstability period for a current bandwidth of a communicative connectionbetween the playback device and a remote system providing thealternative streams in response to a playback request. The playbackdevice then selects one of the alternative streams from which each ofthe portions of the encoded media starting from the playback positioncan be provided prior to a playback time for the portion of encodedmedia during the estimated stability period such that an underflowcondition does not occur during playback of the encoded media. Theplayback device then commences streaming of the encoded media byrequesting the portions of encoded media be transmitted using theselected one of the alternative stream from the remote server. Inaccordance with some of these embodiments, the selected alternativestream also can provide a sufficient number of the portions of theencoded media starting from the playback position prior to an end of theestimated stability period to provide a sufficient buffer duringplayback after the estimated stability period has ended.

The selection of the alternative stream to use is performed in thefollowing manner in accordance with some embodiments of this invention.The selection process begins by selecting of the alternative streams ofencoded media to test. An index of portions of the encoded media for theselected stream is read to determine the size of each of the portions ofencoded media starting from the playback position in the selectedstream. A download time for each of the portions in the selected streamstarting from the playback position is then determined based on the sizeof each of portions. The download time of each of the portions startingfrom the playback position is then compared to the playback time of thedata in each of the portions and to determine whether an underflowcondition occurs during the estimated stability period. If no under flowcondition will occur, the download time of each of the portions iscompared to an end time of the estimated stability period to determinewhether a predetermined number of the portions of the selected stream isreceived prior to the end of the estimated stability period to provide asufficient buffer for playback after the estimated stability period hasended. The stream is then selected if the process determines nounderflow conditions will occur during the estimated stability periodand if a sufficient buffer for playback is provided after the estimatedstability period ends. In accordance with some of these embodiments, theselection of the streams and comparisons are repeated until a stream isselected.

In accordance with some embodiments of this invention, an alternativeselection process is performed in response to a determination that noneof the streams can provide the portions without an underflow conditionand/or without a sufficient buffer at the end of the estimated stabilityperiod. In accordance with some embodiment of this invention thealternative selection process is performed by discarding a first portionfrom each of portions from each stream starting from the playbackposition from consideration and then repeating the selecting of one ofthe alternative streams, comparing of the download time of each of theportions to the playback time of each of the portions, and comparing ofthe download time of each of the of portions for each off the streamswith the end time of the estimated stability period for the alternativestreams with the first portion of each of the first portions discarded.In accordance with other embodiments, the alternative selection processis performed by selecting one of the alternative streams from which toobtain the portions of the encoded media and requiring a predeterminednumber of the portions starting from the playback position be receivedprior to commencing playback of the encoded media.

In accordance with some embodiments of this invention, the selection ofone the alternative streams to test is based on a maximum bitrate ofeach of the plurality of alternative streams. In accordance with someembodiments of this invention the selection process further includesdetermining whether the index of portions for the selected alternativestream is stored by the playback device. If the index is not stored bythe playback device, the index of portions for the selected alternativestream is requested from the remote system. The index of portions of theselected alternative stream is then received by the playback device inresponse to the request.

In accordance with some embodiments of this invention, the estimatedstability period is determined by receiving the estimated stabilityperiod from the remote system. In accordance with other embodiment ofthis invention, the estimated stability period is determined by readinga predefined value for the estimated stability period from a memory ofthe playback device. In accordance with still other embodiments, theestimated stability period is calculated by the playback device frominformation about the communicative connection stored in memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a network diagram of a media streaming system inaccordance with an embodiment of the invention.

FIG. 2 illustrates a block diagram of a playback device that performsprocess for providing systems and methods in accordance with anembodiment of this invention.

FIG. 3 illustrates a flow diagram of a process performed by a playbackdevice for selecting a stream to reduce the amount of buffering neededfor a start-up of playback of the encoded media in accordance withembodiments of this invention.

FIG. 4 illustrates a flow diagram of a process for testing the streamsof encoded media to select a stream in accordance with embodiments ofthis invention.

FIG. 5 illustrates flow diagram of a test process performed on thestreams to determine whether an underflow condition will occur during anestimated stability period and that a sufficient buffer will be providedat an end of the estimated stability period in accordance withembodiments of this invention.

FIG. 6 illustrates a representation of playback time versus streamportion download time to describe an underflow condition in accordancewith embodiments of this invention.

FIG. 7 illustrates the download times for portions of encoded media ofvarious streams versus the estimated stability period and playback timein accordance with an embodiment of this invention.

FIG. 8 illustrates a chart showing bandwidth versus average start-uptime of playback in accordance with an embodiment of this invention.

DETAILED DISCLOSURE OF THE INVENTION

Turning now to the drawings, systems and methods for decreasing aninitial buffering period in an adaptive bitrate system in accordancewith embodiments of the invention are illustrated. Adaptive streamingsystems generally require an initial buffering period in order to obtainenough data of the encoded media to avoid underflow conditions in thelatter parts of the multimedia presentation. For purposes of thisdiscussion, an underflow condition is when a playback device does nothave enough data of the encoded media in a buffer to continue playbackof the encoded media. Typically, this buffering period may apply to theinitial start of the system, as well as after each trick-play or seekoperation. In current playback devices, many stream switching algorithmsenforce a rule involving buffering a predetermined duration of video. Inmany instances, adaptive bitrate streaming systems download portions ofvideo that include closed groups of pictures and can perform streamswitches between closed groups of pictures. Examples of rules involvingbuffering a predetermined duration of video include (but are not limitedto) an 8 second rule used in an adaptive bitrate streaming system thatdownloads closed groups of pictures have 2 second durations. The 8second rule involves the playback device receives enough data of theencoded media to provide 8 seconds of playback prior to commencing theplayback of the encoded media. In accordance with embodiments of thisinvention, systems and methods are provided that allow only one portionof encoded media (i.e. one closed group of pictures), to be receivedprior to commencing the playback. This reduces the start-up time fromthe time needed to receive a specific number of portions of the media tothe time needed to receive a single portion of the media to greatlyenhance the user's enjoyment of the playback of the encoded media.

Streaming System Architecture

Turning now to the FIG. 1, an adaptive streaming system in accordancewith an embodiment of the invention is illustrated. The adaptivestreaming system 10 includes a source encoder 12 configured to encodesource media as a number of alternative streams. In the illustratedembodiment, the source encoder is a server. In other embodiments, thesource encoder can be any processing device including a processor andsufficient resources to perform the transcoding of source media(including but not limited to video, audio, and/or subtitles).Typically, the source encoding server 12 generates a top level index toa plurality of container files containing the streams, at least aplurality of which are alternative streams. Alternative streams arestreams that encode the same media content in different ways. In manyinstances, alternative streams encode media content (such as but notlimited to video) at different maximum bitrates. In a number ofembodiments, the alternative streams are encoded with differentresolutions and/or at different frame rates. The top level index fileand the container files are uploaded to an HTTP server 14. A variety ofplayback devices can then use HTTP or another appropriate statelessprotocol to request portions of the top level index file and thecontainer files via a network 16 such as the Internet.

In the illustrated embodiment, playback devices include personalcomputers 18, CE players, and mobile phones 20. In other embodiments,playback devices can include consumer electronics devices such as DVDplayers, Blu-ray players, televisions, set top boxes, video gameconsoles, tablets, and other devices that are capable of connecting to aserver via HTTP and playing back encoded media. Although a specificarchitecture is shown in FIG. 1, any of a variety of architecturesincluding systems that perform conventional streaming and not adaptivebitrate streaming can be utilized that enable playback devices torequest portions of the top level index file and the container files inaccordance with embodiments of the invention.

Playback Device

The processes for providing methods and systems in accordance with thisinvention are executed by a playback device. The relevant components ina playback device that perform the processes in accordance with anembodiment of the invention are shown in FIG. 2. One skilled in the artwill recognize that playback device may include other components thatare omitted for brevity without departing from this invention. Theplayback device 200 includes a processor 205, a non-volatile memory 210,and a volatile memory 215. The processor 205 is a processor,microprocessor, controller, or a combination of processors,microprocessor, and/or controllers that performs instructions stored inthe volatile 215 or non-volatile memory 210 to manipulate data stored inthe memory. The non-volatile memory 210 can store the processorinstructions utilized to configure the playback device 200 to performprocesses including processes in accordance with embodiments of theinvention and/or data for the processes being utilized. In otherembodiments, the playback device software and/or firmware can be storedin any of a variety of computer readable media appropriate to a specificapplication. Although a specific playback device is illustrated in FIG.2, any of a variety of playback devices configured to store encryptedcryptographic data and to collect information concerning devicecharacteristics can be utilized in accordance with embodiments of theinvention.

Playback Start-Up Process

In accordance with many embodiments of this invention, a process forproviding start-up of a playback process with only a minimal amount ofdata of the encoded media is provided by the playback device. Inadaptive streaming systems, such as the system described with referenceto FIG. 1, the data for the encoded media is generally downloaded inpackets or groups of data that are referred to as portions of encodedmedia for purposes of this discussion. The portions of encoded mediatypically represent a certain amount of playback time. The encoded mediais typically divided based upon the amount of data need for playbackbetween the time needed to switch streams. The portions of encoded mediain the system described with reference to an embodiment of the inventionas shown in FIG. 1 represent 2 seconds of playback time in accordancewith an embodiment of this invention. However, other embodiments maydivide the data based on other amounts of time without departing fromthis invention. In prior art adaptive streaming systems, the start-upalgorithms for playback systems require a certain amount of playbacktime which, in turn, requires that at least a specified number portionsof the encoded data be downloaded prior to the playback being commenced.In accordance with the embodiment shown in FIG. 1, the amount ofplayback time is 8 seconds and 4 portions, each representing 2 secondsof playback time are needed to provide the required data. One skilled inthe art will recognize that other time limits for the playback time andportions may be used depending on the requirements of the system withoutdeparting from embodiments of this invention. The requirement of acertain amount of data to provide a certain amount of playback is toprevent underflow conditions from occurring during playback.

An underflow condition is when the playback device does not have enoughdata of the encoded media stored in a buffer to continue playback. FIG.6 illustrates an underflow condition during playback. Playback periods601 and 602 are the first and second playback periods for playing backthe encoded media. In the system described with reference to FIG. 1,first and second playback periods 601 and 502 are each two second inlength. However, one skilled in the art will recognize that the exacttime of each playback period is dependent on the exact type of adaptivestreaming system used and the above is for exemplary purposes only.First and second download time periods 603 and 604 are the periodsneeded to receive first and second portions of the stream of encodedmedia that provides the data for playback of the encoded media duringfirst and second playback periods 601 and 602. As shown in FIG. 6, thedownloading and playback of the encoded media occur along timeline 600.First download time period 603 is completed prior to the first playbackperiod 601. Therefore, all of the data of the encoded media neededduring first playback period 601 is received prior to first playbackperiod 601. However, second download time period 604 overlaps withsecond playback period 602. Thus, the system has an underflow conditionbecause the second portion of encoded data needed for playback duringsecond playback period 602 is not received prior to the beginning ofsecond playback period 602.

A process performed by a playback device for selecting a stream ofencoded media in an adaptive streaming system such that playback maybegin after receiving one portion of the encoded data of the stream inaccordance with embodiments of this invention is shown in FIG. 3.Process 300 begins by determining an estimated stability period for thebandwidth of the communicative connection between the playback deviceand the remote server providing the streams of encoded data in 305. Thebandwidth is a known bandwidth measure that is known or calculated bythe playback device based upon network and connection conditions. Theestimated period of stability is the time period that the bandwidth isexpected to remain stable. The estimated period of stability variesbased upon the conditions of the network to which the playback device isconnected. In accordance with some embodiments of this invention, theestimated stability period may be a defined value stored in a memory ofthe playback device. In accordance with other embodiments, the estimatedstability period may be calculated by the playback device from datagathered by the playback device while monitoring the current bandwidthand previous conditions stored in a persistent memory of the device. Instill other embodiments, the estimated stability period may be receivedfrom a server that calculates the estimated stability period based onfeedback from the playback device or based upon feedback received from aclass of devices similar to the playback device.

In 310, the playback device tests the streams of encoded media todetermine whether an underflow condition will occur during playback inthe estimated stability period if the stream is used. The streams arealso tested to determine whether a predetermined number of portions ofthe encoded media will be received during the estimated stability periodto provide a sufficient buffer during playback. The predetermined numberis a number of portions that provide data for a specified number ofplayback time periods after the estimated stability period expires. Forexample, a system may require enough portions of data to provide for 4time periods of playback after the end of the estimated stability periodor 8 seconds of playback time in accordance with an embodiment of thisinvention. However, the precise amount of portions and the amount ofplayback time required needed may vary based upon the configuration ofthe system and/or playback device.

A stream is selected to use to receive the portions of the encoded medianeeded for playback at 315. The stream is selected because the testprocess determined that no underflow conditions will occur during theestimated stability period when portions of the encoded media arereceived using the stream. Furthermore, the stream may also satisfy arequirement that at least the predetermined number of portions of theencoded media will be received by the end of the estimated stabilityperiod to provide a sufficient buffer during playback after theestimated stability period in accordance with some embodiments of thisinvention. The buffer can allow the playback device to determine anadequate stream to use to receive portions of the encoded media basedupon the bandwidth conditions after the estimated stability period tocontinue playback. After the stream is selected, the playback devicetransmits a request to the remote server to provide portions of theencoded media using the selected stream in 320. The playback device thenbegins playback of the encoded media after the first portion of theencoded media is received in 325 and process 300 ends.

A process performed by the playback device to test the streams ofencoded media to select a stream that provides portions of the encodedmedia starting from the playback position that do not cause an underflowcondition during playback in the estimated stability period and providesa predetermined number of portions prior to the end of the estimatedstability period to provide a sufficient buffer during playback inaccordance with an embodiment of this invention is shown in FIG. 4.Process 400 begins in 405 by determining whether a portion index foreach of the streams being tested is stored in a memory of the playbackmachine. These portion indexes are typically part of the informationdownloaded by the playback device with the top level index and streaminformation from the container files and provide the size of eachportion of the encoded media in the stream. If the playback device doesnot have a portion index for one or more of the streams, the playbackdevice requests and receives the portion indexes for the streams thatare not stored from the remote server in 410.

In 415, the playback device performs a test process on the streams. Anembodiment of the test process is described below with reference to FIG.5. In 420, process 400 determines whether the test process successfullyselected a stream for use during the startup of playback. If a streamhas been selected by the test process, process 300 ends. If a stream hasnot been selected, process 400 may allow a default process for start-upof playback in 425. If the default process is used, a buffer requirementis set to a maximum predetermined number of portions to provide enoughdata for a certain amount of playback time and a stream of encoded mediais selected. In the embodiment described with reference to FIG. 1, themaximum default buffer is set to 4 portions of the encoded media inorder to provide 8 seconds of playback. However, any number of portionsmay be used and any amount of playback time may be required withoutdeparting from this invention. The exact number of portions and amountof playback time required for the buffer depend on the adaptivestreaming system used.

Alternatively, process 400 may discard the first portion of encoded datafrom each stream in 425 and repeat the test process from 415 using thestream with the discarded first portion. This allows the process to tryto determine a stream that can be used to allow star-up of the playbackof the encoded media after two portions of the encoded media aredownloaded.

A process performed by playback device in 415 of process 400 to select astream in accordance with embodiments of this invention is shown in FIG.5. Process 500 begins in 505 by selecting a stream. In accordance withsome embodiments, the stream may be selected by the maximum bitrate ofeach stream in either ascending or descending order. However, thoseskilled in the art will recognize that other properties of the encodedmedia in the streams, such as resolution and frame rate may also be usedfor the selection of the stream to test without departing fromembodiments of this invention.

After the stream is selected, the portion index for the selected streamis read in 510. Process 400 then determines the portions of the streamstarting from the playback position of the encoded media and the size ofeach portion that may be downloaded during the estimated stabilityperiod in 515. The information about the size of the portions is thenused to determine the download time of each portion of the selectedstream in 520. In 525, the download time of each of the portionsstarting from the playback position is compared to a playback time forthe information to determine whether an underflow condition may occur.If process 500 determines that an underflow condition may occur for theselected stream, a new stream is selected, if available, in 540 andprocess 500 is repeated from 510 for the subsequent stream. If there areno more streams available, process 500 may return an indication thattest process 500 was unsuccessful in selecting a stream.

If process 500 determines that no underflow condition may occur, process500 determines whether a predetermined number of portions of the streamstarting from the playback position of the encoded media may bedownloaded prior to the end of the estimated stability period. If it isdetermined that at least the predetermined number of portions will bedownloaded, the stream will provide a sufficient buffer for playback atthe end of the estimated stability period and process 500 selects thestream for use in 535. Otherwise, a new stream is selected, ifavailable, in 540 is repeated from 510 for the subsequent stream. Ifthere are no more streams available, process 500 may return anindication that test process 500 was unsuccessful in selecting a stream.

Example of Test Process

An illustration of the selection of a stream for use in receivingportions of the encoded media in accordance with an embodiment isprovided with respect to FIG. 7. Four streams, 701-704, that may be usedby a playback device to receive portions of the encoded media forplayback of the encoded media in an embodiment of this invention areshown. The playback device uses the above described process to selectone of streams for use in playback. Streams 701-704 are shown indescending order of maximum bitrates and the streams are selected in thetest process in accordance with maximum bitrates. In the example, thetest process begins be determining the estimated stability period. Theend of the estimated stability period is shown as line 705. The testprocess first reads the index of portions of encoded data of stream 701and determines the download times of the portions starting from theplayback position in the encoded media as shown. The download times arethen compared to the playback times of the portions. As can be seen inFIG. 7, the download time of the second portion of stream 701 does notend prior to the beginning of the second playback time. Therefore, thetest process moves to the next stream with the next highest maximumbitrate, stream 702.

The test process reads the portion index for stream 702 and determinesthe playback times for the portions of encoded media starting from theplayback position as shown in line 702. The playback times of theportions of stream 702 are compared to the playback times. As can beseen in FIG. 7, the download time of the second portion of stream 702does not end prior to the beginning of the second playback time.Therefore, the test process moves to the next stream with the nexthighest maximum bitrate, stream 703. The test process reads the portionindex for stream 703 and determines the playback times for the portionsof encoded media starting from the playback position as shown in line703. The playback times of the portions of stream 703 are compared tothe playback times. As can be seen from line 703, no underflowconditions may occur as all of the portions will be received prior tothe corresponding playback time. Thus, the process determines whether apredetermined number of portions will be received prior to the end ofthe estimated stability period using stream 703. In this case, thestability period ends after the 10^(th) playback period or 20 seconds.Therefore, the stream must be able to provide at least 28 seconds ofplayback or 14 portions of encoded media prior to the end of theestimated stability period. Stream 703 only provides 13 completeportions prior to the end of the estimated stability period. As such,the test process does not select stream 703 for use and selects thestream with next highest maximum bandwidth, stream 704 for testing. Thetest process reads the portion index for stream 704 and determines theplayback times for the portions of encoded media starting from theplayback position as shown in line 704. The playback times of theportions of stream 704 are compared to the playback times. As can beseen from line 704, no underflow conditions may occur as all of theportions will be received prior to the corresponding playback time priorto the end of the estimated stability period. Thus, the test processthen determines whether the predetermined number of portions may bedownloaded prior to the end of the estimated stability period. As seenin line 704, 15 portions of encoded media may be received prior to theend of the estimated stability period. Thus, the test process selectsstream 704 to provide the portions of encoded media for playback asstream 704 will not cause underflow conditions during the estimatedperiod of stability and provides a sufficient buffer at the end of theestimated period of stability.

Improved Playback Start Up Time

FIG. 8 illustrates a chart of playback start-up times for an embodimentin accordance with this invention. In the described embodiment, theadaptive streaming system provides 9 streams. The bandwidth of thecommunicative connection between the playback device and remote serveris varied between 500 Kbps and 10 Mbps. The estimated stability periodfor the bandwidth is 20 seconds and the system has a constant change inseek times. Line 801 shows the selected streams for the playback. Thetime of the start-up is shown be line 802. The bandwidth is shown alongthe x-axis and the time is shown along the y-axis. As can be seen fromthe chart, the average playback start-up time is approximately 1.8seconds after a single portion of the encoded media has been downloaded.This represents a significant improvement over the typical 8 seconds fora conventional playback start-up.

The above is description of embodiments of systems and methods inaccordance with the present invention. It is foreseen that other skilledin the art will design alternative systems that infringe on thisinvention as set forth in the following claims either literally orthrough the Doctrine of Equivalents.

1. (canceled)
 2. A method of determining whether an underflow conditionwill occur in a particular stream of encoded media during a stabilityperiod, the method comprising: requesting playback of content from oneor more servers; estimating the stability period of a communicativeconnection between a playback device and the one or more servers, wherethe estimated stability period is a period of time that thecommunicative connection is expected to remain stable based on bandwidthconditions; selecting one of a plurality of streams of encoded media tobe assessed, where the selected stream comprises encoded media dividedinto a plurality of portions, each portion having the same playbackduration; determining a download time for each of the plurality ofportions based on the size of each of the plurality of portions; anddetermining whether an underflow condition will occur in the selectedstream during the estimated stability period by comparing the determineddownload time of each of the plurality of positions to the playbackduration of each of the plurality of portions and accumulating thedifference.
 3. The method of claim 2, wherein selecting one of theplurality of streams of encoded media to be assessed comprises selectingthe stream of encoded media with the highest maximum bit rate.
 4. Themethod of claim 3, wherein selecting one of the plurality of streams ofencoded media to be assessed, determining a download time for each ofthe plurality of portions, and determining whether an underflowcondition will occur in the selected stream is repeated until a streamis selected where an underflow condition will not occur.
 5. The methodof claim 4, wherein the next selected one of the plurality of streams ofencoded media to be assessed is the stream of encoded media with thenext highest maximum bit rate.
 6. The method of claim 2, whereindetermining the download time for each of the plurality of portionscomprises reading an index of portions of the selected stream of encodedmedia to determine the size of each of the plurality of portions of thestream of encoded media.
 7. The method of claim 2, further comprising:discarding a first portion from each of the plurality of portions of theselected stream from consideration in response to a determination thatthe plurality of portions of the stream of the encoded media cannot beprovided using any of the plurality of streams prior to playback timeduring the estimated stability period; and repeating the steps ofselecting one of the plurality of streams, determining a download timefor each of the plurality of portions without the first portion, anddetermining whether an underflow condition will occur without the firstportion.
 8. The method of claim 2, further comprising performing analternative selection process for selecting one of the plurality ofalternative streams in response to a determination that an underflowcondition will occur during the estimated stability period.
 9. Themethod of claim 2, further comprising, in response to a determinationthat an underflow will occur in all of the plurality of streams duringthe estimated stability period, requiring a predetermined number of theplurality of portions be received prior to commencing playback of theencoded media.
 10. The method of claim 2, wherein determining theestimated stability period comprises receiving the estimated stabilityperiod from the one or more servers.
 11. The method of claim 2, whereindetermining the estimated stability period comprises reading apredefined value for the estimated stability period from a memory of theplayback device.
 12. A playback device for playing back a stream ofencoded media comprising: a memory; a processor configured via a clientapplication stored in the memory to: request playback of content fromone or more servers; estimate a stability period of a communicativeconnection between a playback device and the one or more servers, wherethe estimated stability period is a period of time that thecommunicative connection is expected to remain stable based on bandwidthconditions; select one of a plurality of streams of encoded media to beassessed, where the selected stream comprises encoded media divided intoa plurality of portions, each portion having the same playback duration;determine a download time for each of the plurality of portions based onthe size of each of the plurality of portions; and determine whether anunderflow condition will occur in the selected stream during theestimated stability period by comparing the determined download time ofeach of the plurality of positions to the playback duration of each ofthe plurality of portions and accumulating the difference.
 13. Theplayback device of claim 12, wherein selecting one of the plurality ofstreams of encoded media to be assessed comprises selecting the streamof encoded media with the highest maximum bit rate.
 14. The playbackdevice of claim 13, wherein selecting one of the plurality of streams ofencoded media to be assessed, determining a download time for each ofthe plurality of portions, and determining whether an underflowcondition will occur in the selected stream is repeated until a streamis selected where an underflow condition will not occur.
 15. Theplayback device of claim 14, wherein the next selected one of theplurality of streams of encoded media to be assessed is the stream ofencoded media with the next highest maximum bit rate.
 16. The playbackdevice of claim 12, wherein determining the download time for each ofthe plurality of portions comprises reading an index of portions of theselected stream of encoded media to determine the size of each of theplurality of portions of the stream of encoded media.
 17. The playbackdevice of claim 12, wherein the processor is further configured via theclient application stored in the memory to: discard a first portion fromeach of the plurality of portions of the selected stream fromconsideration in response to a determination that the plurality ofportions of the stream of the encoded media cannot be provided using anyof the plurality of streams prior to playback time during the estimatedstability period; and repeat the steps of selecting one of the pluralityof streams, determining a download time for each of the plurality ofportions without the first portion, and determining whether an underflowcondition will occur without the first portion.
 18. The playback deviceof claim 12, wherein the processor is further configured via the clientapplication stored in the memory to perform an alternative selectionprocess for selecting one of the plurality of alternative streams inresponse to a determination that an underflow condition will occurduring the estimated stability period.
 19. The playback device of claim12, wherein the processor is further configured via the clientapplication stored in the memory to, in response to a determination thatan underflow will occur in all of the plurality of streams during theestimated stability period, require a predetermined number of theplurality of portions be received prior to commencing playback of theencoded media.
 20. The playback device of claim 12, wherein determiningthe estimated stability period comprises receiving the estimatedstability period from the one or more servers.
 21. The playback deviceof claim 12, wherein determining the estimated stability periodcomprises reading a predefined value for the estimated stability periodfrom a memory of the playback device.